1. Field of the Invention
The present invention relates to a vehicular controller having a monitoring function, more specifically, it relates to a vehicular controller that has a control CPU and a monitoring CPU for monitoring the control CPU and for detecting an abnormal status of the control CPU.
2. Description of Related Art
A micro controller is used for a vehicular controller such as an engine control unit (ECU) for controlling operating conditions of an engine. The ECU may have a main CPU and a sub-CPU. FIG. 8 shows an arrangement of the ECU 20 that has main CPU 21 and sub-CPU 22. The main CPU 21 and the sub-CPU 22 shares engine control tasks. For example, main CPU 21 executes a fuel injection control and an ignition control. The sub-CPU 22 executes a throttle control. In the throttle control, sub-CPU 22 controls an electromagnetic actuator to operate a throttle valve a target opening degree that is determined in accordance with an operating degree of an accelerator pedal. The main CPU 21 and the sub-CPU 22 communicates with each other via an appropriate communication means such as a Universal Asynchronous Receiver Transmitter (UART), and shares data for executing respective control tasks. The CPUs 21, 22 shares data such as signals from sensors.
The main CPU 21 also executes a monitor control for monitoring status of the sub-CPU 22. For example, main CPU 21 monitors a watch dog pulse (WD pulse) from sub-CPU 22, and detects an abnormal status of die sub-CPU 22 based in deviation in periodicity of the watch dog pulse. In case of a detected abnormal status of sub-CPU 22, main CPU 21 resets sub-CPU 22.
The sub-CPU 22 also executes a monitor control for monitoring status of the main CPU 21, such as whether several control processes and communication processes are executed properly. The watch dog circuit 23 inputs a watch dog pulse from the main CPU 21, and resets the main CPU 21 if the periodicity of the watch dog pulse goes out of a proper cycle.
In order to monitor the status of the main CPU 21, sub-CPU 22 needs to hold monitoring data such as data indicative of an abnormal status or data indicative of a parameter threshold. For this purpose, for example, monitoring data may be stored in a mask ROM, and sub-CPU 22 reads out monitoring data from the mask ROM. However, the monitoring data may be varied in each engine or vehicle. Therefore, the mask ROM is inconvenient for such a variable data memory.
Alternately, the monitoring data may be preset in hardware circuits. For example, a plurality of combinations of the monitoring data may be preset in the hardware circuit, and sub-CPU 22 may select an appropriate combination out of the plurality of combinations. The hardware circuit may be arranged to output a plurality of analogue voltage signals. In such a case, only a limited number of combinations of the monitoring data are available, and additional hardware circuits such as an A/D converter and port are needed.
In addition, rapidly increasing capacity and improving processing performance of the CPU enables a single CPU to executes a plurality of control processes such as engine control and throttle valve control processes. Conventionally, the engine control process includes a fuel injection control process and an ignition control process. However, in order to ensure a reliability of throttle control, a small capacity and low performance CPU may be used as a monitoring CPU for monitoring purpose only. In such an arrangement, the same disadvantages as described above still exit.